This invention relates to a method for rapidly charging a battery in as short a time as possible.
There are essentially two types of related art battery charging methods which rapidly charge a battery. The first type of charging method charges a battery with a constant current until full charge is reached. This charging method is adopted for nickel hydrogen batteries and nickel cadmium batteries. This charging method detects peak battery voltage or a ΔV voltage drop from the peak battery voltage to determine full charge and terminates charging. The second type of charging method performs constant voltage charging after constant current charging, and is adopted for lithium ion batteries. This charging method detects voltage rise until a charging termination voltage is reached, then full charge is assumed and charging is terminated.
These types of charging methods continuously charge primarily while detecting battery voltage. However, battery temperature rises during charging, and batteries have the property that performance degrades when battery temperature becomes abnormally high. To avoid this drawback, a charging method has been developed which also detects battery temperature and controls charging current to keep battery temperature from becoming abnormally high and charging efficiency from decreasing (Patent Reference 1: Japanese Non-examined Patent Publication HEI 7-15884 (1995)).
In the charging method cited in this disclosure, rechargeable battery temperature is detected, and the duty factor of the pulse charging current is changed in an effort to decrease battery temperature rise. If a battery is charged with constant current, battery temperature rises as shown by curve A of FIG. 1. As shown by curve A, battery temperature rises sharply as full charge is approached. Curve B of FIG. 1 shows variation in battery voltage during charging. In curve B, the battery is fully charged when battery voltage reaches its peak voltage, or after a ΔV voltage drop from the peak voltage. Based on this, the battery has the property that temperature rises radically when full charge is approached. If battery temperature becomes high, it causes battery performance degradation. When battery temperature is high, the charging method cited in the disclosure above reduces the duty factor of the charging current to prevent performance degradation due to high battery temperature. As shown by the solid line of FIG. 2, battery temperature rise is moderated by this action. In particular, temperature rise at full charge can be reduced. Consequently, battery performance degradation due to battery temperature rise at full charge can be prevented.